1. Field of the Invention
The present invention generally relates to printer control devices for use with printer mechanisms operated by host computers, and more particularly to a method and apparatus for selecting and controlling certain printer processing steps in accordance with the type of recording media present within the printer, especially for multiple paper-type POS printers. The invention further relates to a printer structure that utilizes an efficient command interface to achieve desired printing operations in association with the type of recording medium or paper being used.
2. Related Technological Art
The market for retail store automation equipment is developing rapidly with the widespread introduction of point-of-sale (POS) terminals, even for smaller establishments. Point-of-sale systems have also become indispensable within the distribution of goods and service industries. Centralized and satellite, that is personal-type, computers have been incorporated into such systems to achieve uniform control over output and centralized information tracking functions. This computerization is expected to create increased demand in the future for standardized peripheral devices for point-of-sale and related systems. But a look at the point-of-sale environment as a whole reveals a number of deficiencies which need to be addressed.
Unfortunately, many competing POS-type terminal printers use mutually incompatible interfaces and command structures or language. As a result, the range of applications for POS-type printers and equipment has remained limited and equipment costs relatively high. In response, some methods are being developed to control and check the status of specialized point-of-sale printers using standard or existing computer interfaces.
One such standard interface that has been in use within the personal computer industry for a number of years is the so-called "Centronics" parallel interface. First introduced by the Centronics company, this particular interface has proven very popular, and there is worldwide agreement in the computer industry as to what this interface protocol consists of and how to properly connect to it. Another popular computer interface is the RS-232 serial interface, which is generally employed with computer peripherals such as modems, scanners, or digitizers. Once the most common interface in personal computer printers, the Centronics parallel interface has given way in some areas to faster, more flexible, or higher data transfer rate interfaces of which the SCSI and Appletalk interfaces are examples. However, so-called IBM compatible computers and POS equipment still make heavy use of the Centronics parallel interface. At least one company, Seiko Epson Corporation of Tokyo is promulgating an alternative interface protocol for a parallel interface which is called "ESC/P" or "ESC/POS."
A major problem with the Centronics interface is that it was defined at a time when there was no reason to provide for more than one paper status indication or "paper empty" status signal. Early computer operators simply needed to know whether or not any paper was present. Therefore, a single paper status signal line was provided for on one pin, designated as pin number 12, in a 25 pin standardized electrical connector format, and used to transfer a signal labeled as the "PE" signal, indicating a paper empty condition. The PE signal uses a High logic level output value to indicate when the printer has run out of paper, whenever paper end detection is enabled. Unfortunately, this renders newer POS printers, which can accommodate a variety of different paper types, hard to control because the paper status of each type or source of paper cannot be individually determined. A POS host computer or control system in such a situation is forced to assume recording paper is ready for output, when very often it is not, with deleterious results.
A second problem is that computer or POS-type printers provide limited control over vertical line advance or spacing. POS-type printers have a single memory element or storage location for storing information such as a setting or parameter defining the amount by which paper is to be advanced when changing to print on successive lines of the paper, the so-called line spacing setting. Once a value for line spacing is stored in memory, the stored value is used for whatever type of paper is inserted into the printer until it is reset or changed to a new value. Therefore, it is necessary for the host computer to expend resources tracking the type of paper being used and resetting the line spacing value every time the paper type is changed. This places an increased burden on host computer resources and its communication facilities and detrimentally decreases printing speed.